Broad and tunable second harmonic generation from 250 to 430 nm from a 80 MHz picosecond white light source

Supercontinuum generation in microstructured fibers is a most versatile method to generate a wide range of visible to near infrared colors from fixed wavelength femto- and picosecond sources. Since photonic crystal structures lead to a favorable zero-dispersion wavelength close to the pump wavelength, high fiber lengths can be used. As a consequence, nJ pulse energies out of MHz repetition rate oscillators are sufficient for the spectral broadening. So far, however, the shortest wavelengths that are readily achieved are just slightly below 400 nm. For many applications in biology and chemistry, e.g., fluorescence lifetime imaging (FLIM), total internal reflection fluorescence (TIRF) microscopy or single molecule imaging, light in the UV - as far down as 250 nm for DNA bases - is needed. No UV generation from either laboratory or commercial "white light lasers" (WLL), i.e. a combination of ps pump laser with photonic fiber, has been reported.